Microarray technology is known to be useful in monitoring levels of gene expression. Microarrays include regions of either different polynucleotides or antibodies arranged in a predetermined configuration and bound on a substrate. These regions are positioned at specific locations on the substrate. In a typical experiment, a sample of total RNA, mRNA, or proteins are collected from two individuals or under two treatment conditions. In use, when exposed to a sample from an individual or a under a specific treatment condition, the array will exhibit an observed binding pattern of the cDNA (mRNAs reverse transcribed) or proteins to the bound DNA or antibodies, respectively. A basic principle of the microarray is the differential labeling of two samples (e.g., by radio-labeling or fluorescent dyes) and observing the intensities of each sample at each location in the microarray. Using this technique, an investigator can determine whether specific genes are upregulated or downregulated in various individuals and under various treatment conditions. By using a single reference sample as a control for a series of experimental samples, the investigator can compare relative levels of expression among the treatment samples.
In one format, microarray analysis is conducted on an examination slide, such as microscope slide or a diagnostic plate. Such examination slides generally are made from clear glass or plastic, but may be made of other materials. For higher throughput studies, an investigator will conduct several microarray assays on a single microscope slide. Under such circumstances, however, with ordinary manipulation and processing of the slide during the microarray process, liquid from one sample on the slide may spill over or migrate, and mix with another sample on the slide. Accordingly, various barriers have been developed to prevent contamination between multiple samples on a microarray slide. Known products for separating samples on a slide include rubber gaskets, with or without adhesive, hydrophobic markers known as PAP pens, and manufactured barriers such as Teflon®. There are problems with these products, however: gaskets without adhesive do not seal well; when gasket adhesive is used, it can be dissolved by solvents and interfere with experiments; hydrophobic pens are tedious, difficult to use accurately, and dissolve in certain detergents and solvents; and manufactured barriers are expensive and inflexible. Also, gaskets need to be removed before scanning in a typical laser scanner (and some slide coatings will peel off when the gasket is removed). Microarray scanners commonly have clearance for the slide and sample of approximately 250 micrometers.